Electrodeless gaseous electric discharge devices utilizing ferrite cores



March 10, 1970 J. M. ANDERSON ELECTRODELESS GASEOUS ELECTRIC DISCHARGEDEVICES UTILIZING FERRITE CORES 2 Sheets-Sheet 1 Filed July 17, 1967 CONVER TER 7'0 RAD/0 FREQUENCY Inna/21701: John er-son,

71's Attorney- United States Patent US. Cl. 315-57 9 Claims ABSTRACT OFTHE DISCLOSURE A gaseous discharge light source includes anon-conducting light transmissive hermetically sealed envelope in theform of a closed loop containing an ionizable gas. Envelope iselectromagnetically coupled to a source of RE. energy, generating powerat a frequency, preferably of 100 kc. to 500 kc., by a ferrite core.Energy source comprises a low cost solid state oscillator circuitproducing a relatively low voltage. Envelope may be coated on theinterior thereof with a fluorescent phosphor emitting visible light whenirradiated by excited specie of the ionizable gas. Instantaneousstarting is achieved by inducing a high starting voltage into theenvelope by a step-up secondary winding on the ferrite core.

The present invention relates to improved gaseous electric dischargedevices and more particularly to such devices in which electrodes areeliminated.

The electric lamp technology has long sought electric discharge deviceswhich produce visible light for general illumination purposes withoutthe utilization of electrodes as the foot-points of a glow or aredischarge. Although the concept of electrodeless discharge lamps is veryold, such lamps have always included the concept of coupling electricalenergy into an hermetically sealed gaseous containing envelope by meansof a ferro-magnetic or air core transformer to avoid the use ofelectrodes. Such devices have never proved practical or commerciallyfeasible, because it has been impossible to achieve any reasonableefficiency of light emission due to the utilization of iron or air coretransformers because of core losses, among other factors.

Accordingly it is an object of the present invention to provide improvedelectrodeless gaseous arc discharge apparatus.

Another object of the present invention is to provide fluorescent lampapparatus in which the sole limitation placed upon the operation of thelamps is the inherent limitation of efiiciency in the lamp phosphoritself.

Yet another object of the present invention is to provide a gaseouselectrode discharge light source and a low-cost, low-voltage powersupply therefor.

Still another object of the present invention is to provide gaseous arcelectrodeless discharge devices and sim ple and inexpensive means forinstantaneously initiating operation thereof.

Briefly stated, in accord with one embodiment of the present invention,I provide efiicient electrodeless gaseous discharge device light sourceswherein an evacuable and hermetically sealed envelope forms a closedloop which forms the secondary of a transformer. The envelope is filledwith an ionizable vapor capable of emitting radiant energy when excitedand'ionized either for illumination purposes or for the excitation of aluminescent phosphor. Energy is coupled into the vapor containingenvelope by means of a ferrite core having relatively low losses atradio frequencies of higher than 50 kilocycles per second. The primarywinding upon the ferrite core is connected with a low cost, solid stateoscillator circuit, producing electromagnetic oscillations at radiofrequencies in excess p CC of approximately 50 kc. and preferably in therange of to 500 kilocycles at a relatively low volt-age, the order ofmagnitude of the voltage necessary to cause operation of the lamp.

In accord with a preferred embodiment of the present invention theinterior of the evacuable envelope is coated with a luminescent phosphorwhich is excited to emission of visible light by absorption of radiationemitted by the excited ionizable vapor within the envelope. In furtheraccord with another preferred embodiment of the present invention,instantaneous starting of the vapor discharge lamp is achieved by asecondary winding on the ferrite core which couples a very high startingvoltage into the vapor containing envelope.

The novel features believed characteristic of the present invention areset forth in the appended claims.

The invention itself, together with further objects and advantagesthereof, may best be understood with reference to the following detaileddescription taken in connection with the appended drawing in which:

FIG. 1 illustrates, in perspective, a luminaire including a light sourceconstructed in accord with the present invention,

FIG. 2 illustrates, partially in schematic and partially in verticalcross-section, the device of FIG. 1 and the operating voltage source,

FIG. 3 illustrates in vertical cross-section an alternative embodimentto the device of FIG. 1,

FIG. 4 illustrates a horizontal cross-sectional view of the device ofFIG. 3,

FIG. 5 illustrates yet another alternative embodiment of the invention,

FIG. 6 illustrates a further alternative for the arrangement of theferrite core in accord with the present invention, and

FIG. 7 illustrates a schematic circuit for an inexpensive radiofrequency oscillator constructed in accord with the present invention.

In FIG. 1, a lighting fixture indicated generally as 10 includes areflecting shield 11 having supported therein an hermetically sealed,hollow, tubular envelope 12 supported upon support clamps 13 and 14.Envelope 12 is encircled by a pair of annular ferrite cores 15 and 16which are coupled to a source of electromagnetic energy (not shown).

FIG. 2 illustrates, partially in cross-section and partially in blockschematic diagram, the apparatus illustrated in FIG. 1. In FIG. 2,evacuable envelope 12 is surrounded by core 15, and core 16 (shieldedfrom view). Core 15 is wound with a plurality of turns 17 of wire whichare connected to radio frequency oscillator 19 energized from aconventional 60 cycle alternating current source 20. In practice, core15 serves as the coupling member of a transformer of which winding 17constitutes the primary and ionized vaporized material within envelope12 constitutes a one-turn secondary. As is illustrated in FIG. 1 of thedraWings,a plurality of coupling cores may be utilized to energizesimultaneously the ionizable vapors within envelope 12. The core primarywindings for the plurality of circuit may be connected in series,parallel, or series parallel circuit relationship with no impedancematching problems.

The device of FIG. 1 and the cross-sectional view of FIG. 2 illustratesone embodiment of the invention wherein a high intensity light sourcemay be desired. In the alternative, it may be desirable that a householdfixture, which may be substituted for a conventional fluorescent lamputilizing ballast transformers and electrodes, be provided.

For utilization in a conventional household installation, a deviceillustrated in vertical section in FIG. 3 may be utilized. In FIG. 3 acase 21 which may contain radio frequency oscillator 19 is utilized tosupport cores 15 and 16 about which are wound primary windings foractivation of the ionizable vapors within envelope 12.

In FIG. 4 of the drawing a plan view, taken from below the device ofFIG. 3, illustrates how such an arrangement may conveniently be utilizedto substitute for a conventional fluorescent fixture wherein elongatedenvelope 12 is substituted for a pair of parallel conventionalfluorescent lamps.

Envelope 12 is filled with a suflicient quantity of mercury to provide avapor pressure, at an operating temperature of approximately 40 C., ofapproximately 5 to and preferably 7 microns and is filled to excess toinsure such partial pressure. For example, an envelope having a volumeof approximately 30' cubic inches was filled with 50 milligrams ofmercury to provide a suitable operating partial mercury vapor pressure.For purposes of starting an electric discharge within envelope 12, apartial pressure argon of approximately 1 to 5 and preferablyapproximately 2.5 millimeters of mercury is added. In the lamp describedabove, 2.5 millimeters of argon was used. Radio frequency oscillator 19produces oscillations within the frequency range of 100 to 500kilocycles per second and provides a relatively low voltage output ofthe order of 50 to 100 volts RMS alternating current at currents ofapproximately 0.25 to 1.0 ampere. The above lamp was excited with 400kilocycle radio frequency oscillations, applying to the ionized vaporwithin the single turn of the secondary voltage of approximately 70volts. Since the lamp had a path length of approximately 35 inches inlength, the voltage gradient along the discharge path was approximately2 volts per inch. Suitable operating voltage gradients are in the rangeof 0.5 to 5 volts per inch. The current measured by a sensing coilindicated a current within the arc of approximately 0.5 ampere. Underthese circumstances, the calculated heating loss within ferrite core and16 was approximately 9 watts and amounted to, on the basis of a powerinput of 42 watts, a loss of approximately 21% In accord with thepresent invention utilizing ferrite cores I am able to provide highefficiency light from an ionizable gaseous source when the core loss isanything less than 50%.

I am aware that it has been proposed in the prior art to exciteelectrodeless gaseous discharge lamps using electromagnetic induction totransfer electric energy into the discharge vessel. Experiments alongthis line disclose that heretofore such means have been highlyimpracticable. If an air core transformer is utilized, the inefficiencyof the coupling procedure in order to achieve a reasonable power inputto the gaseous discharge results in a loss of power by radiation whichis prohibitive, and which may be dangerous. Accordingly such deviceshave never been successfully operated for useful periods at anyreasonable efliciency.

Another alternative that has been proposed in the prior art is theutilization of an iron or ferromagnetic cores. Such cores, however, maybe utilized only on very low frequencies in order that heating of theiron and eddy currents do not cause core failure. Utilizing alternatingcurrent, it is exceedingly diflicult to operate an iron core transformerfor the purpose of transferring energy of this nature at frequencies inexcess of 5 or 10 kilocycles per second. Based upon experimental andcalculated results obtained at this laboratory, it has been determinedthat for an iron core transformer operating at 50 kilocycles infrequency, core losses in power are in the range of approximately 80 to90%. Accordingly, from the foregoing it may readily be appreciated thatair core and iron core transformers are, from a practical point of view,inoperative to operate at the high radio frequency voltages incurreucethat I find necessary for efficient operation of gaseous discharge lampsin accord with the invention.

In accord with a preferred embodiment of the present invention, theinterior surface of the envelope 12 is coated with a conventionalfluorescent phosphor such as a calcium halo-apatate, which phosphors arewell known to the art. These phosphors are capable of absorbing theultraviolet radiation of mercury which is generally peaked at about 2537AU and, upon stimulation thereby, emitting radiation within the visiblespectrum to produce a highly eflicient and pleasing light output. Inthis embodiment of the invention, the electric discharge is not reliedupon to produce the light emission, but rather, to produce radiationwhich causes light to be emitted from a luminescent phosphor. Thisallows for a relatively low power input to the ionizable gas since thegas itself is not relied upon for the necessary light emission but onlyfor radiation to Stimulate the phosphor.

Lamps constructed in accord with the preferred embodiment of the presentinvention are highly useful in that the electrodes which are the sourceof many of the limitations in present day fluorescent lamps areeliminated. Thus, for example, burnout of an electrode can never be thecause of a failure of a lamp in accord with the present invention.Similarly, sputtering of electrode materials upon the interior surfaceof the lamp walls, causing darkening thereof, is completely eliminated.Likewise, and of equal importance, the problems of metal to glass orceramic seals are completely eliminated. In electric discharge lamps ofthe prior art, emphasis has been placed, in obtaining greaterefficiencies, in producing lamp envelopes fabricated from material whichwill withstand higher operating temperatures, as for example, fusedquartz, high density alumina and similar ceramic materials. With thesematerials the differential coefficient of expansion between the lampenvelope and tungsten, nickel and other metals conventionally utilizedto pass electric leads through the envelopes becomes an increasinglydiflicult problem. A high proportion of lamp failures, in the mostsophisticated designs, result from failure of a metal to glass or metalto quartz or ceramic seal. In accord with the present invention, allelectrodes within the envelope are eliminated and, likewise, all metalto glass, Pyrex or ceramic seals, thus eliminating one of the greatestcauses of lamp failure.

In accord with a further embodiment of the present invention, I providean instantaneously starting lamp. As is well known to the art, althougha relatively low voltage is sufficient to maintain a gaseous arcdischarge in operation, once the arc has been struck, a high voltage isgenerally required to cause initial breakdown. This is so, even in thepresence of a readily ionizable inert gas, such as argon, to cause aninitial breakdown to facilitate ionization of mercury, the commondischarge carrying metallic vapor utilized in gaseous vapor dischargelamps. In many instances, this high voltage for starting is provided bya mechanical starter, with capacitive or inductive elements, whichsuddenly separates causing a high voltage surge to electrodes of thedevice in order to cause initial ionization. Alternative arrangementsinvolve the use of ballast transformers to provide the necessaryvoltage. In accord with the present invention, I find that this problemmay be rapidly, inexpensively and easily solved by my discovery that anauxiliary secondary winding upon the ferrite core, with suflicient turnsto cause it to operate as a step-up secondary, may be utilized to tapoff a very high voltage which may be applied to the lamp to cause theinduction of a high starting voltage, which rapidly causes the initialbreakdown necessary for operation of lamps in accord with the presentinvention.

The aforementioned starting means is illustrated in greaterparticularity in FIG. 3 of the drawing wherein, at the broken apartportion of the left end of the fixture, core 15 may be seen to beencircled by a large number of turns constituting an auxiliary secondarywinding 22, which is connected with a pair of spaced probes 23 and 24which are in contact with respective portions of the lamp envelope 12 onthe side thereof that is away from the direction of light propagation.Alternatively, the probes may enter the envelope, although generallythis is to be avoided because of seal problems. Conveniently, in theaforementioned embodiment of the invention wherein the primary windingon ferrite core 15 constituted 3 turns, a turn auxiliary secondary 22was utilized to cause a voltage of approximately 2000 peak-to-peak voltsto be applied to cause instantaneous starting. This instantaneousstarting arrangement has the advantage over other instantaneous startingarrangements in that it requires no auxiliary member which must separateto cause a high voltage transient and the high voltage is applied to thelamp at all times, but without any deleterious effect, even with longlife lamp operation.

FIG. 5 of the drawing illustrates an alternative embodiment of theinvention wherein a single core may be utilized, with or withoutadditional cores in parallel, to energize a single fluorescent lampwhich has a Figure 8 shape with a common central leg, or wherein a pairof loops may pass through the same core or cores to be energized therebysimultaneously. In FIG. 5, envelopes 25 and 26 having energized legs 27and 28, respectively, pass through 3 ferrite cores 29, 30 and 31, eachof which is wound, either in series circuit or series-parallelrelationship, depending upon the impedance match desired for theenergizing circuit, with primary windings to cause the coupling of anappropriate voltage to the portions 27 and 28 of envelopes 25 and 26constituting single turn secondaries of the effective transformer tocause the initiation of breakdown therein. In order that both envelopes25 and 26 break down, auxiliary cores 32 and 33 are used and, aresimilarly energized in order to make sure that ionization occurs in bothenvelopes. In their absence, ionization in one core, would.

cause a lower voltage gradient therein thus effectually short-circuitingthe unionized envelope so that only one would be energized. With thepresence of cores 32 and 33, however, both envelopes are energized,ionized, and both emit visible radiation.

FIG. 6 of the drawing illustrates yet another embodiment of theinvention, wherein the structure of a core utilized is such as to allowfor removal of the lamp envelope in case of failure thereof by breakage,or by extended life and burnout of the phosphor, or any othercontingency which may occur. In FIG. 6 a primary winding 17 wraps arounda portion of core and couples electromagnetic energy into envelope 12.As is also illustrated in FIG. 3, a second secondary 22, having a largenumber of windings as compared with primary winding 17, is connectedwith a pair of probes 23 and 24 which are connected with, and abuttingagainst, the outer edges of envelope 12 to cause a high voltage to beinduced therein to cause initial breakdown of the ionizable vaporstherein. A portion 35 of core 17 is hinged at 36 and fastened at 37 topermit opening of the closed core to remove the envelope 12 and replacewith a new one. Although the particular shape of core 17 illustrated inFIG. 6 is square, it should be appreciated that any configuration ofcore may be hinged to permit removal thereof, and that the fact thatthere is an interface between respective portions of the core is of noreal significance in utilizing the core to couple electromagnetic energyfrom primary 17 to the vapors within envelope 12.

FIG. 7 of the drawing illustrates schematically a radio frequencyoscillator which is utilized, in accord with the the fluorescent lampembodiment of the present invention, to provide a radio frequency signalof approximately 400 kilocycles per second for operation of lampenvelope 12 containing an ionizable mixture of argon and mercury, asdescribed above. In FIG. 7, envelope 12 is electromagnetically coupledby four ferrite cores, each of which is represened by a single dottedline, paired for purposes of simplicity of representation, in coregroupings 40 and 41. Core groupings 40 and 41 are coupled in a primarywinding arrangement constituting first coil members 42 and 43 and secondcoil members 44 and 45. Coil members 42 and 43 are each wound in seriescircuit relationship around the core members constituting core grouping40, on one hand, and the cores of core grouping 41, on the other hand,and are connected in parallel relationship with a 0.03 microfaradcapacitor to provide a resonant circuit. Coil members 44 and 45 are eachwound in series circuit relationship around both of the cores withineither core grouping 40 or core grouping 41 and are then connected inparallel circuit relationship with one another. Coils 44 and 45 areconnected in the emitter circuit of the transistor 46, utilized as theactive circuit element in the oscillator of FIG. 7. In the specificembodiment constructed and illustrated in FIG. 7, an M1423 transistorwas utilized as transistor 46, which is connected in a modified Hartleyoscillator configuration, connected in the grounded-collector,emitter-fed circuit configuration. A similar, collector fedconfiguration could also be used.

The emitter circuit of transistor 46 also includes an MR1337-3 diode toprotect the transistor emitter circuit. The input to the transistorcircuit is approximately volts DC. and is provided by a rectifying andfilter network represented generally as 50 which is connected with a 117volts A.C. RMS voltage source. This filter and rectification networkincludes a 2.5 ohm, 5 watt input resistor and a bridge networkcomprising 4 symmetrical IRIODBSA germanium diodes shunted with a 200microfarad capacitor. In operation, coil members 42 and 43 are connectedin series circuit relationship across all of the cores in core groupings40 and 41 to keep the voltage induced thereby in phase. Each of coils 42and 43 may conveniently consist of a single turn about each core. Theactual driving power for each core is supplied by coil members 44 and 45which effectively constitute the primary windings for the cores and mayconveniently be from 3 to 6 windings about each core member connected asillustrated in FIG. 7. Alternatively, a modified circuit may be utilizedwherein a similar oscillator utilizes a pair of transistors connected ina modified push-pull oscillator circuit for added power and stability.

In accord with the present invention, it is necessary that the coresutilized be of such material and configuration that the core losses areno greater than 50% in order that effective coupling of electromagneticenergy into the light source may be effected. Similarly, low core lossesreduce heating of the core and minimize the possibility of failure andmaximize its efliciency. Preferably, as in the described specificembodiment of the invention hereinbefore, core losses are maintained toless than 25% of total input power. The amount of core utilized varieswith the degree of excitation required. In general, however, in orderthat a voltage gradient of 2 volts RMS per inch be induced in anenvelope having an arc length of approximately 36 inches, I find that itis necessary to use approximately 4 square inches in cross section ofcore, the exact configuration of the closed loop of the core beingimmaterial. In general, any high performance, low loss ferrite corematerial may be utilized. As is Well known to the art, a ferrite is aceramic-like material showing ferri-magnetic properties and usuallyexhibits a spinel structure having a cubic crystal lattice and has thegeneralized formula Me-Fe O wherein Me represents any metal. A suitablecore material may be obtained from Ferrox Cube Company of Saugerties,N.Y., and may bear the identification Type 3B7 or Type 3H1. Such cores,having an annular configuration with an outside diameter of 3 /2 inchesand an inner diameter of 1 /2 inches, have been utilized in accord withthe present invention. To drive a 1% inch outside-diameter fluorescentlamp having a partial pressure of 7 microns of mercury and a partialpressure of argon of 2 /2 mm. of mercury, four such cores have beenutilized, each core having a thickness dimension of approximately inch.Accordingly, two square inches cross section of total core utilized,resulting in a 55 volt arc drop at 0.5 ampere and a core loss oftotalling approximately 10 watts at a total input power of 42 watts anda 25% core loss.

By the foregoing it may readily be seen that I have discovered a new andimproved method of providing electrodeless arc lamps and, morespecifically, fluorescent arc lamps wherein the light emitted thereby isemitted by a fluorescent phosphor coating the interior surface of alight-transmissive, non-conducting hermetically sealed envelopecontaining a partial pressure of mercury and an inert starting gas. Inaccord with my invention, I provide an electromagnetic coupling betweena radio frequency oscillator oscillating in a frequency range of from100 kilocycles per second to 500 kilocycles per second utilizing ferritecores having a power efficiency such as to keep the core losses below50% and preferably below 25%. In further accord with my invention Iprovide a solid state oscillator producing radio frequency oscillationsin the range of 100 kilocycles to 500 kilocycles per second anddelivering an output power that is relatively low.

In further accord with the present invention I am able to cause a lampconstructed in accord with the present invention to be instantaneouslystartable, by providing a second secondary winding upon the ferritecore, which winding is a step-up winding and is connected with a pair ofprobes upon the exterior surface of the lamp envelope, causing theinduction of a high voltage therein which is sufficient to causeinstantaneous starting of the lamp.

While the invention has been set forth hereinbefore with respect tocertain specific embodiments thereof many modifications and changes willreadily occur to those skilled in the art. Accordingly by the appendedclaims I intend to cover all such modifications and changes as fallwithin the true spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric light producing apparatus including (a) a hollow tubularlight transmissive envelope in the form of a closed loop containing anionizable vapor,

(b) coupling means encircling a portion of said loop and comprising ahigh frequency high ferrimagnetic permeability ferrite core adapted tocouple energy from an input winding to said ionizable vapor at a radiofrequency in excess of approximately 50 kc. with less than 50% loss ofenergy.

() an input winding encircling a portion of said coupling means forsupplying an alternatnig radio frequency voltage of in excess ofapproximately 50 kc. thereto,

(d) means connected to said input winding for generating a radiofrequency voltage at a frequency in excess of approximately 50 kc.

2. The apparatus of claim 1 wherein the radio frequency is in the rangeof approximately 100 kc. to 500 kc.

3. The apparatus of claim 2 wherein said envelope is coated on theinside thereof with a luminescent phosphor adapted to emit light in thevisible spectrum when excited by radiation of a mercury arc and saidenvelope further includes sufiicient mercury to supply an excess ofunvaporized mercury under operating conditions and a partial pressurethereof of approximately 5 to 10 microns and a partial pressure thereinof an inert gas of approximately 1 to 5 torr.

4. The apparatus of claim 3 wherein the coupling coefilcient and theefiiciency of the transformer comprising said ferrite core, saidionizable vapor, and said primary winding is effective to produce avoltage within said ionizable vapor from 50 to volts RMS A.C. at acurrent of 0.25 to 1.0 ampere and a radio frequency of 100 to 500kilocycles per second.

5. The apparatus of claim 3 wherein the voltage gradient within saidionized vapors within said envelope is approximately 0.5 to 5.0 voltsper inch.

6. The apparatus of claim 3 wherein said radio frequency generatingmeans is a modified Hartley oscillator in the grounded collector circuitconfiguration with output feed to said core.

7. The apparatus of claim 5 wherein a first primar winding for supplyingpower to a plurality of cores is wound in series parallel circuitrelationship about said plurality of cores and a second control andfeedback primary winding is wound around each of said plurality of coresin series circuit relationship to maintain phase synchronization betweensaid cores.

8. The apparatus of claim 2 wherein a second secondary winding encirclessaid ferrite core with a greater number of turns than said primarywinding and the ends thereof are connected to probes attached adjacentthe exterior of said envelope for inducing therein a high voltage tocause instantaneous energization of said ionizable vapors therein uponenergization of said primary winding.

9. The apparatus of claim 7 wherein said starting voltage isapproximately 500 to 1000 volts RMS.

References Cited UNITED STATES PATENTS 1,534,251 4/1925 Smith 315-248 X1,813,580 7/1931 Morrison -2 315248 X 2,030,957 2/1936 Bethenod et a1.315248 2,770,734 11/1956 Reek 331-117 X JAMES W. LAWRENCE, PrimaryExaminer C. R. CAMPBELL Assistant Examiner US. Cl. X.R.

